This study will test the hypothesis that the circadian rhythm of sleep is altered in major depressive disorder (MDD) compared to age and sex matched control subjects. It will focus on coordination of wakefulness to sleep. It is hypothesized that sleep onset differences will include: 1)higher beta & lower delta EEG activity; 2)elevated core body temperature, a decreased rate of decline in core body temperature; 3)delayed melatonin secretion, increase cortisol secretion, diminished sleep-related growth hormone secretion.